Changes

Sometimes the companies re-release the games digitally, as a wrapper containing an emulator and the ROM. Depending on the company, the ROM may or may not be directly playable in regular emulators. You can extract those ROMs and play them without having to go to shady sites nor tracking expensive cartridges and potentially breaking them in the ripping process. And you get to support the company who made the stuff you love, instead of resellers hoarding second-hand game copies or random ROM sites. That being said, emulated re-releases may contain changes due to licensing or censorship issues amongst other things.